Earthquake early warning systems use earthquake science and the technology of monitoring systems to alert devices and people when shaking waves generated by an earthquake are expected to arrive at their location. The seconds to minutes of advance warning can allow people and systems to take actions to protect life and property from destructive shaking. The U.S. Geological Survey (USGS), in collaboration with several partners , has been working to develop an early warning system for the United States. ShakeAlert, a system currently under development, is designed to cover the West Coast States of California, Oregon, and Washington. Earthquakes pose a serious risk to our Nation. According to the Federal Emergency Management Agency (FEMA), 77 percent of that risk, or an average annual loss of $4.1 billion, is concentrated on the West Coast in Cali-fornia, Oregon, and Washington (Federal Emergency Management Agency, 2008). Growing urbanization and increasing reliance on complex infrastructure for power, water, telecommunication, and transportation magnify that risk. An earthquake early warning system that can rapidly detect earthquakes and send alerts could prompt actions to protect life and property before strong shaking arrives. Development of such a system is a critical step toward offsetting physical risks, improving public understanding of earthquake hazards, and reducing fear of the unknown and unpredictable nature of earthquakes. An earthquake occurs when a fault in the Earth's crust slips suddenly and the two sides move relative to one another. The rupture begins at one point on the fault and rapidly extends along some distance of the fault, like a lengthening crack in a car windshield. As the rupture travels along the fault, the sudden movement of the two sides of the fault generates seismic (shaking) waves that radiate outward through the Earth-much like ripples from a stone dropped in water. It is these waves that cause the ground shaking you can feel and the damage and destruction during earthquakes. Although no one can predict earthquakes , the technology exists to provide warning to surrounding communities once a quake begins. This is done by an Sensors positioned about 6-12 miles apart Earthquake alert center Sensors Epicenter P-wave S-wave Fir st F e lt W a v e Dam ag in g W a v e s Fault Epicenter Earthquake early warning systems like ShakeAlert work because the warning message can be transmitted almost instantaneously, while shaking waves from the earthquake travel through the Earth at speeds of a few miles per second. When an earthquake occurs, seismic waves-including compressional (P) waves, transverse (S) waves, and surface waves-radiate outward from the epicenter. The faster but weaker P waves trip nearby sensors, causing alert signals to be sent out, giving people and automated electronic systems some time (seconds to minutes) to take protective actions before the arrival of the slower but stronger S waves and surface waves. Computers and mobile phones receiving the alert message can calculate the expected arrival time and intensity of shaking at your location. USGS image created by Erin Burkett (USGS) and Jeff Goertzen (Orange County Register).
Burkett, E. R., Given, D. D., Jones, L. M., Erin R. Burkett, Given, D. D., & Jones, L. M. (2014). ShakeAlert-An Earthquake Early Warning System for the United States West Coast. U.S. Geological Survey Fact Sheet, (February). Retrieved from https://pubs.usgs.gov/fs/2014/3083/pdf/fs2014-3083.pdf%0Ahttps://pubs.er.usgs.gov/publication/fs20143083